Post-quantum computing
cryptography analysis

Security of encryption and hashing algorithm rely on computational
unfeasibility of solving some classes of hard mathematical problems in
reasonable time and with finite / cost effective computation resources.
Quantum computing, based on quantum bits (qbits) which can exist in
superpositions of states, provides breakthrough performances in
solving some classes of hard mathematical problems over classic
computing methods, based on binary digital electronic architecture;
the impact of this performance improvement must be carefully evaluated
to assess
security of existing cipher and hash functions in a scenario where
quantum computers will be available.
Under current understandings, the impact of increasingly more powerful
quantum computers with increasingly larger number of qbits has very
different degrees of impact on feasibility to reduce / break security
of algorithms commonly employed in symmetric-key
or public-key cryptography.

Quantum
computing and symmetric-key encryption algorithms

To
preserve data secrecy, symmetric-key cryptography rely on a shared
secret element (password / passphrase, keyfile, biometric data, or
combinations of more factors as in two-factor authentication) between
two or more parties.
The need to share this element, needed by receiver for decryption, is
the main
disadvantage of (secret) symmetric-key cryptography solutions over
public-key cryptography solutions.
PeaZip currently supports only symmetic-key
encryption mechanisms, using password / passphrase and optionally
two-factor authentication (password / passphrase + key file), which
under current understandings are quite
secure against attacks by
arbitrarily sized quantum computers.
Grover's quantum algorithm is the best-possible known attack for most
of current generation symmetric encryption algorithms (and hash
functions), providing - for NP-complete problems - a quadratic speed-up
over a classic computing based brute-force search.
Consequently, as a general rule, doubling the size of a symmetric key
can
effectively make up for the increase of efficiency of Grover's
algorithm over classic brute-forcing, and block these attacks.
In example, under those premises
AES 256 bit could be considered equivalent in security (when
arbitrarily large quantum computers are available, using Grover
algorithm over the 256 bit key space) to AES 128 bit (for
classic computers, using classic computing brute-force over the 128 bit
key space).
While a quadratic speed-up (providing a sufficiently powerful quantum
computer is available) is an huge performance improvement, it is
nowhere near a complete breakthrough as polynomial time solution
provided by Shor's algorithm is for public-key encryption systems, so
post-quantum symmetric
cryptography is thought to not need to differ significantly from the
current generation.Learn more: Grover's
algorithm

Quantum
computing and public-key encryption algorithms

Public-key
encryption systems are currently extremely popular, as they
simplify key exchange task: anyone can encrypt a message using a public
key released by a receiver, but only receiver's private key can decrypt
messages protected by its public key.
Unfortunately, most ones of currently popular public-key algorithms are
susceptible of being efficiently broken by a large enough quantum
computer.
Shor's quantum algorithm runs in polynomial time to solve hard
mathematical problems used in most common public-key encryption
(integer
factorization problem, discrete logarithm problem, elliptic-curve
discrete logarithm problem), rather than in exponential or
sub-exponential time as the best, most efficient classic algorithms.
Experimenting public-key algorithms relying on problems not efficiently
simplified by Shor's algorithm or other quantum algorithms, being both
reasonably safe under classic computing and quantum computing -based
attacks, is currently an active research topic in cryptography.PeaZip currently does not
support public-key encryption methods, only
symmetric (secret) -key encryption - keys (passwords, keyfiles) needs
to be privately, securely shared with receiver for decryption to take
place.Learn more: Shor's
algorithm
.

Please note quantum
cryptography is a
separate topic, studying how to
apply quantum phenomena to cryptography in order to achieve
secrecy and detect
eavesdropping, rather than analyzing how
quantum computers
characteristics affects safety (in terms of computational
feasibility
of attacks or brute-forcing) of encryption / hashing algorithms - the
topic discussed in this page and properly named post-quantum
cryptography

Read more about symmetic-key encryption algorithms supported by PeaZip:
Rijndael/AES
(implemented as AES128 and AES256 in 7Z, ARC, PEA, and ZIP standards),
and Twofish and Serpent ciphers
(implemented for ARC and PEA standards).
Read more about cryptographically
secure hash function